The present invention relates to the combination of a manhole closure assembly and a separate support ring, and more particularly to a closure and ring combination that prevents drainage and storm water from emptying into a manhole that leads to a sewerage system.
It is desirable to segregate sanitary or sewerage systems from those systems designed to handle storm and drainage water since such segregation reduces an unnecessary burden on the sewerage treatment facility. Obviously, when drainage and storm water empties into a sanitary system the sewerage treatment plant must necessarily handle and treat the storm water in addition to the sewerage material. Standard frames and covers for manholes that lead to sanitary or sewerage systems generally include heavy cover constructions with passageways therein that serve to vent the overall system for the purpose of relieving internal pressure as well as vacuum build-ups. The passageways in these manhole covers also enable storm water to empty into the sewerage system. It is impossible to simply seal off or otherwise eliminate the cover passageways since pressure developed within the sewerage system could easily produce a force sufficient to blow the cover away from its seated position at the manhole opening or blast the plugs away from the passageways. Additionally, pressure developed within the sewerage system can easily cause damage to the system if that pressure is not relieved.
With an oversized sewerage or sanitary system, storm water draining into the system does not present any significant problems. On the other hand, with many existing systems capacity is already at peak level, and it is estimated that 40 percent of that capacity is the direct result of storm or drainage water. For the most part, storm water volume draining into sewerage systems is much more acute today than it was many years ago, and the key factor is that today there is significantly less pervious area than there was even several years ago. This factor is due to larger impervious street areas that collect more drainage water as well as smaller building lot sizes which cut down on the amount of overall pervious area. Such factors have significantly contributed to the problem of overtaxing present sewerage systems. By significantly preventing storm and drainage water from emptying into such systems, existing facilities can easily handle an additional 60% or more sewerage capacity.